Severe Weather Discussion – 2008-9-1

– Active severe weather expected this afternoon and tonight across much of Oklahoma northward into Nebraska. Primary threats are tornadoes, destructive hail, and strong winds.

– Chase Status is increased to Level 4.

Discussion:

Little time for a discussion, attempting to spin up on the weather features today.

Northern stream longwave trof is taking shape just west of the region this afternoon. This feature will continue moving east the remainder of today into tonight. Afternoon surface analysis shows a dryline in western Oklahoma with a windshift boundary farther east. Winds across the western parts of Oklahoma westward to the dryline are slightly veered at 200 degrees. Winds in central sections are more 170 to 180 degrees. Temperatures are commonly in the upper 70s to low 80s with dewpoints in the mid 60s. This is yielding CAPE values near 3200 J/Kg in parts of central Oklahoma, with LIs to -7. Low and mid level wind speed/directional shear are quite favorable for rotating updrafts and organized storms.

Two parameters are of concern at this point. 1) is the EML, cap. However, CIN values are below 25J?kg as of 19z and only a little more cap erosion is needed for storm initiation. As such, the cap is not expected to be a problem and may help things as it keeps storms isolated. 2) Upper level winds. To me this is the biggest limiting factor we face right now as these winds are generally 40-60kts across the state. However, one bright side is the WSW to ENE orientation of the mean 300/200mb flow. This should limit anvil seeding and the overall expected isolated nature of storms should help also.

The NWS is focusing on northern Oklahoma where low level shear will be best. However, I think there is a general threat along the I-35 corridor, especially near Oklahoma City given the 3400 J/Kg CAPE max just southwest of the metro at 19z. This is the primary reason we’re going to hug I-40 today. Things could get real interesting around 19:00-20:00 as the low level jet develops.

Probabilities:

None

Chase Status:

Level 4 – Heading to Weatherford around 16:00.

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